Efficacy of Different Isolates of Entomopathogenic Fungi against Brevicoryne brassicae (Linnaeus) at Different Temperatures and Humidities

Abstract

The virulence of twenty-five isolates of entomopathogenic fungi consisting of ten belonging to Beauveria bassiana (Bills.) Vuill., seven to Verticillium lecanii (Zimmerman), five to Metarhizium anisopliae (Mctschinikoff) Sorokin, two to Nomnraea rileyi (Farlow) Samson and one to Paecilomyces fumosorosens (Wize) Brown and Smith originating from a wide range of insect species was investigated in laboratory bioassays on cabbage aphid, Brevicoryne brassicae (Linnaeus) at different regimes of temperature (20, 25 and 30°C) and relative humidity (75, 85, 90 and 95%). All fungal isolates except N. rileyi isolates were pathogenic to the aphid, but in varying degrees. Among three levels of temperature tested, aphid mortality was significantly higher at 25°C than 20 and 30°C. Aphid mortality decreased with decreasing relative humidity. Among all isolates in all combinations of temperature and relative humidity, four isolates of V. lecanii, V.I-l, V.I-2, V.l-6, and V.I-7.showed higher virulence to B. brassicae. In multiple dose bioassays, lowest LT₅₀ was obtained from V.1-7 isolate. The highest virulence of V.1-7 isolate of V. lecanii to B. brassicae suggests that the isolate would be a potential candidate as a microbial control agent for the cabbage aphid.